Referring to FIG. 8, a conventional sewing machine 1 is mounted on a desktop 7, comprises a motor 8 for driving the sewing machine 1 for sewing clothes, which motor 8 is installed beneath the desktop 7. The motor 8 comprises a rotor shaft 81 having a belt rotor 82. An endless belt 83 is mounted around the rotor 82 and a belt roller 84, this arrangement is disposed on the outside of the sewing machine 1. As the motor 8 is electrically energized, the rotor shaft 81 rotates the rotor 82, which in turn will transmit the power through the endless belt 83 to rotatably drive the belt roller 84. The belt roller 84 rotatably drives the sewing shaft for driving the sewing needle of the sewing machine 1 to start the process of stitching the clothes. However, in order to install the belt 83, the belt 83 needs to pass through the desktop 7, and thus it is difficult to assemble and/or disassemble the belt 83.
According to another conventional design, a motor 9 is installed behind the sewing machine 1 (as shown in FIG. 9). An endless belt 93 is mounted around a rotor 91 of the motor 9 and a belt roller 92 to rotatably drive the sewing shaft of the sewing machine 1. However, in both of the above-mentioned prior art arrangements, it is essential that tightness of the belt should be well adjusted for proper power transmission. In other words, if the tightness of the belts 83 and 93 is not well adjusted, then the power transmission from motor 8 and 9 through the belts 83 and 93 to drive sewing shaft of the sewing machine 1 is not sufficient. This will cause break downs or damage to the sewing mechanism of the sewing machine 1. Further, after a long-time of operation of the belts 83 and 93, the belts 83 and 93 losses some elasticity, and thus tightness of the belts are not sufficient to effectively drive the sewing shaft of the sewing machine 1.
Furthermore, in prior art U. K. Patent GB 2135345 entitled motor-driven sewing machine, discloses that the motor is installed inside the frame together with other assembly parts such as sewing shaft and its rotation mechanism for operating the sewing machine and controlling the motor through an external controlling device. The other conventional sewing machine APW297 was manufactured by JUKI, which has a motor installed at an upper part inside the frame of the sewing machine. Still some have taken the center of gravity into consideration with a view of stable operation of the sewing machine, and accordingly proposed to install the motor at a rear upper part inside the frame of the sewing machine. These latter two designs of sew machine could incur extra labor cost due to difficulty in assembling the assembly of parts, and also it is very difficult to remove the motor from inside the frame of the sewing machine for replacement or repair when damage to the motor occurs. This design causes problems during maintenance and increases the cost due to long maintenance interruptions.